Abstract To survive, living organisms must collect information about their environment and use it to select appropriate behaviors. However, information from the environment is often noisy, incomplete and ambiguous. Currently, no theory or model comprehensively explains how nervous systems solve the problem of navigation based on noisy information. Without such a theory, we cannot improve the ability of living systems or autonomous machines to make better decisions by processing the imperfect sensory information that is typically available to them. We propose to build a complete data-driven model of how nervous systems turn noisy sensory information into action selection during navigation. We have previously been able to decipher aspects of this process by studying the Drosophila melanogaster larva ? a small, transparent organism that is exceptionally good at navigating towards food odors despite having only 10,000 neurons. My lab has developed methods to rigorously quantify odor landscapes; measure how neurons represent these odors; automatically track larval movement; create virtual sensory realities for the larva; and change the real-time behavior of the larva on- demand with optogenetics. We have also recently mapped an entire pathway within the larval nervous system. Here, we will determine how and when noisy sensory information causes the larva to reorient (stop and turn) as it is navigating towards an attractive odor source (chemotaxis). Our objective is to uncover the neural mechanisms that accumulate, filter, and process noisy sensory evidence and use ambiguous information to make coherent perceptual decisions (action selection). By combining theory, experiments, and modeling, we will iteratively build a quantitative model which predicts the cellular and circuit-level computations transforming sensory (olfactory) signals into navigational decision-making (chemotaxis) that is robust to environmental disturbances (noise).